Thank you arn, thank you. A reasonable question.
If it works fine under a tower, we can't say much.
If the effect is reproducible under the tower, then we can hypothesize that there is something going on that shouldn't be, and then we have made progress.
We can't disprove, we can only prove. Either it will prove there is an issue, or it will not. It will not prove there is not an issue.
an "issue" is often defined as " A matter of public concern ", this is public concern that their phones won't work while using them every where but under a cell tower.